Add "sensor" to entity listener

This needs to be done so that all information about the contact is known
in an entity listener. Previously, the listener had no information about
*which* fixture on the entity was being contacted.
Fix error caused by previous commit
Rename variables to be more clear

LoserContactListener no longer only deals with Sensors, so the names of
the contacting fixtures have been changed to reflect this.

EntityListener just had flat out wrong names
Make processFixture public

So that it may be called manually instead of beginContact or endContact,
which requires a Contact object
Change visibility of LoserContactListener to protected

Player needs to access it in order to fix its contacts when it turns its
alternate bodies off
Let player fix its contacts whenever its body is switched

The Player class switches bodies internally, which keeps endContact from
being called. endContact isn't called when a body is set to inactive.
Therefore, Player needs to manually manage a list of its contacts and
call processFixture (begin = false) whenever it switches bodies. 

Note, this commit does not call the method to flush contacts yet
Move anonymous class to private nested class PlayerContactFixerListener

Needed in order to call the method to flush the leftover contacts from
within Player